Why are carbohydrates and nucleic acid protein molecules. What came before: nucleic acid or protein. What foods are rich in fats
What elements prevail in the composition of living organisms?
Why are molecules of proteins, nucleic acids, carbohydrates and lipids considered as biopolymeters only in the cell?
What is meant by the word universality of biopolymeter molecules?
a) the sequence of alternating amino acids
b) the number of amino acids in the molecule
c) the form of the tertiary structure
d) all the specified features
3. In what case is the DNA nucleotide composition indicated correctly?
a) ribose, phosphoric acid residue, thymine
b) phosphoric acid, uracil, deoxyribose
c) the remainder of phosphoric acid, deoxyribose, adenine
d) phosphoric acid, ribose, guanine
4. Monomers of nucleic acids are:
a) nitrogenous bases
b) ribose or deoxyribose
c) deoxyribose and phosphate groups
d) nucleotides
5. Amino acids in a protein molecule are linked by:
a) ionic bond
b) peptide bond
c) hydrogen bond
d) covalent bond
6. What is the function of the transport RNA?
a) transfers amino acids to ribosomes
b) transfers information from DNA
c) forms ribosomes
d) all the listed functions
7. Enzymes are biocatalysts consisting of:
a) proteins b) nucleotides c) lipids c) fats
8. Polysaccharides include:
a) starch, ribose
b) glycogen, glucose
c) cellulose, starch
d) starch, sucrose
9. Carbon as an element is a part of:
a) proteins and carbohydrates
b) carbohydrates and lipids
c) carbohydrates and nucleic acids
d) all organic compounds of the cell
10. The cell contains DNA:
a) in the nucleus and mitochondria
b) in the nucleus, cytoplasm and various organelles
c) in the nucleus, mitochondria and cytoplasm
d) in the nucleus, mitochondria, chloroplasts
WHAT IS A NUCLEIC ACID MONOMETER? OPTIONS (AMINO ACID, NUCLEOTIDE, PROTEIN MOLECULE?) WHAT IS INCLUDED INNUCLEOTIDE COMPOSITION
OPTIONS: (AMINO ACID, NITROGEN BASE, PHOSPHORIC ACID RESIDUE, CARBOHYDRATE?)
Help me please!1.Science studying cells is called:
A) Genetics;
B) Selection;
C) ecology;
C) Cytology.
2. Organic matter of the cell:
A) Water, minerals, fats;
B) Carbohydrates, lipids, proteins, nucleic acids;
C) Carbohydrates, minerals, fats;
D) Water, minerals, proteins.
3. Of all organic substances, the bulk in the cell is:
A) Proteins.
B) Carbohydrates
C) Fats
D) Water.
4. Replace the highlighted words with one word:
A) Small molecules of organic substances form complex molecules in the cell.
B) Constant structural components of the cell perform functions vital for the cell.
C) The highly ordered, semi-liquid internal environment of the cell provides for the chemical interaction of all cellular structures.
D) The main photosynthetic pigment imparts a green coloration to chloroplasts.
5. The accumulation and packaging of chemical compounds in the klek is carried out:
A) Mitochondria;
B) Ribosomes;
C) Lysosomes;
D) Golgi complex.
6. The functions of intracellular digestion are performed by:
A) Mitochondria;
B) Ribosomes;
C) Lysosomes;
D) Golgi complex.
7. "Assembly" of a polymeric protein molecule is produced by:
A) Mitochondria;
B) Ribosomes;
C) Lysosomes;
D) Golgi complex.
8. The set of chemical reactions resulting in the decomposition of organic substances and the release of energy is called:
A) Catabolism;
B) anabolism;
C) Metabolism;
D) Assimilation
9. "Copying" genetic information from a DNA molecule by creating i-RNA is called:
A) Broadcast;
B) Transcription;
C) Biosynthesis;
D) Glycolysis.
10. The process of formation of organic matter in the light in chloroplasts using water and carbon dioxide is called:
A) Photosynthesis;
B) Transcription;
C) Biosynthesis;
D) Glycolysis.
11. The enzymatic and anoxic process of decomposition of organic substances is called:
A) Photosynthesis;
B) Transcription;
C) Biosynthesis;
D) Glycolysis.
12. What are the main provisions of the cell theory.
Current page: 2 (total of the book has 16 pages) [available passage for reading: 11 pages]
Biology - the science of life is one of the oldest sciences. Man has been accumulating knowledge about living organisms for thousands of years. As knowledge accumulated, biology was differentiated into independent sciences (botany, zoology, microbiology, genetics, etc.). The importance of borderline disciplines connecting biology with other sciences - physics, chemistry, mathematics, and others - is growing more and more. As a result of integration, biophysics, biochemistry, space biology, and others arose.
At present, biology is a complex science, formed as a result of the differentiation and integration of different disciplines.
In biology, various research methods are used: observation, experiment, comparison, etc.
Biology studies living organisms. They are open biological systems that receive energy and nutrients from the environment. Living organisms react to external influences, contain all the information they need for development and reproduction, and are adapted to a certain habitat.
All living systems, regardless of the level of organization, have common features, and the systems themselves are in continuous interaction. Scientists distinguish the following levels of organization of living nature: molecular, cellular, organismic, population-specific, ecosystem and biosphere.
Chapter 1. Molecular level
The molecular level can be called the initial, deepest level of organization of living things. Every living organism consists of molecules of organic substances - proteins, nucleic acids, carbohydrates, fats (lipids), called biological molecules. Biologists are investigating the role of these essential biological compounds in the growth and development of organisms, storage and transmission of hereditary information, metabolism and energy conversion in living cells and in other processes.
In this chapter, you will learn
What are biopolymers;
What is the structure of biomolecules;
What are the functions of biomolecules;
What are viruses and what is their peculiarity.
§ 4. Molecular level: general characteristics
1. What is a chemical element?
2. What is called an atom and a molecule?
3. What organic substances do you know?
Any living system, no matter how complex it is organized, manifests itself at the level of functioning of biological macromolecules.
By studying living organisms, you learned that they are composed of the same chemical elements as non-living ones. More than 100 elements are currently known, most of which are found in living organisms. The most common elements in living nature include carbon, oxygen, hydrogen and nitrogen. It is these elements that form the molecules (compounds) of the so-called organic matter.
All organic compounds are based on carbon. It can bond with many atoms and their groups, forming chains of different chemical composition, structure, length and shape. From groups of atoms, molecules are formed, and from the latter, more complex molecules, differing in structure and functions. These organic compounds that make up the cells of living organisms are called biological polymers or biopolymers.
Polymer (from the Greek. polys - numerous) - a chain consisting of numerous links - monomers, each of which is relatively simple. A polymer molecule can consist of many thousands of interconnected monomers, which can be the same or different (Fig. 4).
Fig. 4. Diagram of the structure of monomers and polymers
The properties of biopolymers depend on the structure of their molecules: on the number and variety of monomer units that form the polymer. All of them are universal, since they are built according to the same plan for all living organisms, regardless of species.
Each type of biopolymer has a specific structure and function. So, molecules proteins are the main structural elements of cells and regulate the processes occurring in them. Nucleic acids participate in the transfer of genetic (hereditary) information from cell to cell, from organism to organism. Carbohydrates and fats are the most important sources of energy necessary for the life of organisms.
It is at the molecular level that all types of energy are converted and metabolized in the cell. The mechanisms of these processes are also universal for all living organisms.
At the same time, it turned out that the various properties of biopolymers that make up all organisms are due to various combinations of just a few types of monomers that form many variants of long polymer chains. This principle underlies the diversity of life on our planet.
The specific properties of biopolymers are manifested only in a living cell. Isolated from cells, biopolymer molecules lose their biological essence and are characterized only by the physicochemical properties of the class of compounds to which they belong.
Only by studying the molecular level, one can understand how the processes of the origin and evolution of life on our planet proceeded, what are the molecular bases of heredity and metabolic processes in a living organism.
The continuity between the molecular and the next cellular level is ensured by the fact that biological molecules are the material from which supramolecular - cellular - structures are formed.
Organic matter: proteins, nucleic acids, carbohydrates, fats (lipids). Biopolymers. Monomers
Questions
1. What processes are scientists investigating at the molecular level?
2. What elements prevail in the composition of living organisms?
3. Why are molecules of proteins, nucleic acids, carbohydrates and lipids considered as biopolymers only in the cell?
4. What is meant by the universality of biopolymer molecules?
5. How is the diversity of properties of biopolymers that are part of living organisms achieved?
Tasks
What biological patterns can be formulated based on the analysis of the text of the paragraph? Discuss them with your class members.
§ 5. Carbohydrates
1. What substances related to carbohydrates do you know?
2. What role do carbohydrates play in a living organism?
3. As a result of what process carbohydrates are formed in the cells of green plants?
Carbohydrates, or saccharides, Is one of the main groups of organic compounds. They are part of the cells of all living organisms.
Carbohydrates are made up of carbon, hydrogen and oxygen. They got the name "carbohydrates" because most of them have the same ratio of hydrogen and oxygen in the molecule as in the water molecule. The general formula of carbohydrates is C n (H 2 0) m.
All carbohydrates are divided into simple ones, or monosaccharides, and complex, or polysaccharides (fig. 5). Of the monosaccharides, the most important for living organisms are ribose, deoxyribose, glucose, fructose, galactose.
Fig. 5. The structure of the molecules of simple and complex carbohydrates
Di- and polysaccharides are formed by combining two or more monosaccharide molecules. So, sucrose (cane sugar), maltose (malted sugar), lactose (milk sugar) - disaccharidesformed by the fusion of two monosaccharide molecules. Disaccharides are similar in properties to monosaccharides. For example, both are water soluble and have a sweet taste.
Polysaccharides are composed of a large number of monosaccharides. These include starch, glycogen, cellulose, chitin and others (fig. 6). With an increase in the amount of monomers, the solubility of polysaccharides decreases and the sweet taste disappears.
The main function of carbohydrates is energetic... During the breakdown and oxidation of carbohydrate molecules, energy is released (during the breakdown of 1 g of carbohydrates - 17.6 kJ), which ensures the vital activity of the body. With an excess of carbohydrates, they accumulate in the cell as reserve substances (starch, glycogen) and, if necessary, are used by the body as an energy source. Increased breakdown of carbohydrates in cells can be observed, for example, during seed germination, intense muscle work, prolonged fasting.
Carbohydrates are also used as building material... Thus, cellulose is an important structural component of the cell walls of many unicellular organisms, fungi and plants. Due to its special structure, cellulose is insoluble in water and has high strength. On average, 20–40% of the plant cell wall material is cellulose, and cotton fibers are almost pure cellulose, which is why they are used to make tissues.
Fig. 6. Scheme of the structure of polysaccharides
Chitin is part of the cell walls of some protozoa and fungi, and it is also found in certain groups of animals, for example, in arthropods, as an important component of their external skeleton.
Complex polysaccharides are also known, consisting of two types of simple sugars, which regularly alternate in long chains. Such polysaccharides perform structural functions in the supporting tissues of animals. They are part of the intercellular substance of the skin, tendons, cartilage, giving them strength and elasticity.
Some polysaccharides are part of cell membranes and serve as receptors, allowing cells to recognize each other and interact.
Carbohydrates, or saccharides. Monosaccharides. Disaccharides. Polysaccharides. Ribose. Deoxyribose. Glucose. Fructose. Galactose. Sucrose. Maltose. Lactose. Starch. Glycogen. Chitin
Questions
1. What is the composition and structure of carbohydrate molecules?
2. What carbohydrates are called mono-, di- and polysaccharides?
3. What functions do carbohydrates perform in living organisms?
Tasks
Analyze Figure 6 "Scheme of the structure of polysaccharides" and the text of the paragraph. What assumptions can you make based on a comparison of the molecular structure and functions performed by starch, glycogen and cellulose in a living organism? Discuss this issue with your classmates.
§ 6. Lipids
1. What fatty substances do you know?
2. What foods are rich in fat?
3. What is the role of fats in the body?
Lipids (from the Greek. lipos - fat) - an extensive group of fat-like substances, insoluble in water. Most lipids are composed of high molecular weight fatty acids and the trihydric alcohol glycerol (Fig. 7).
Lipids are present in all cells without exception, performing specific biological functions.
Fats - the simplest and most widespread lipids - play an important role as energy source... When oxidized, they provide more than twice as much energy as carbohydrates (38.9 kJ for the breakdown of 1 g of fat).
Fig. 7. The structure of the triglyceride molecule
Fats are the main form lipid storage in a cage. In vertebrates, about half of the energy consumed by cells at rest comes from fat oxidation. Fats can also be used as a source of water (oxidation of 1 g of fat produces more than 1 g of water). This is especially valuable for arctic and desert animals living in conditions of a lack of free water.
Due to their low thermal conductivity, lipids perform protective functions, that is, they serve for thermal insulation of organisms. For example, in many vertebrates, the subcutaneous fat layer is well expressed, which allows them to live in cold climates, and in cetaceans it also plays another role - it contributes to buoyancy.
Lipids perform and building function, since insolubility in water makes them essential components of cell membranes.
Many hormones (for example, the adrenal cortex, genital) are lipid derivatives. Therefore, lipids are inherent regulatory function.
Lipids. Fats. Hormones. Lipid functions: energy, storage, protective, construction, regulatory
Questions
1. What substances are lipids?
2. What is the structure of most lipids?
3. What functions do lipids perform?
4. What cells and tissues are most rich in lipids?
Tasks
After analyzing the text of the paragraph, explain why many animals before winter, and anadromous fish tend to accumulate more fat before spawning. Give examples of animals and plants in which this phenomenon is most pronounced. Is excess fat always good for the body? Discuss this problem in class.
§ 7. Composition and structure of proteins
1. What is the role of proteins in the body?
2. What foods are rich in protein?
Among organic substances proteins, or proteins, Are the most numerous, most diverse and of primary importance biopolymers. They account for 50–80% of the dry mass of the cell.
Protein molecules have big sizesso they are called macromolecules... In addition to carbon, oxygen, hydrogen and nitrogen, proteins can include sulfur, phosphorus and iron. Proteins differ from each other in number (from one hundred to several thousand), composition and sequence of monomers. Amino acids are the monomers of proteins (Fig. 8).
An endless variety of proteins is created by various combinations of only 20 amino acids. Each amino acid has its own name, special structure and properties. Their general formula can be represented as follows:
An amino acid molecule consists of two parts identical for all amino acids, one of which is an amino group (-NH 2) with basic properties, the other is a carboxyl group (-COOH) with acidic properties. The part of the molecule called the radical (R) has a different structure for different amino acids. The presence in one molecule of the amino acid of the basic and acidic groups determines their high reactivity. Through these groups, amino acids are combined to form protein. In this case, a water molecule appears, and the released electrons form peptide bond... Therefore proteins are called polypeptides.
Fig. 8. Examples of the structure of amino acids - monomers of protein molecules
Protein molecules can have different spatial configurations - protein structure, and in their structure, four levels of structural organization are distinguished (Fig. 9).
The amino acid sequence in the polypeptide chain is primary structure squirrel. It is unique to any protein and determines its shape, properties and function.
Most proteins have the form of a helix as a result of the formation of hydrogen bonds between CO and NH-groups of different amino acid residues of the polypeptide chain. Hydrogen bonds are weak, but together they provide a fairly strong structure. This spiral - secondary structure squirrel.
Tertiary structure - three-dimensional spatial "packing" of the polypeptide chain. The result is a bizarre but specific configuration for each protein - globule... The strength of the tertiary structure is provided by a variety of bonds that arise between amino acid radicals.
Fig. 9. Scheme of the structure of a protein molecule: I, II, III, IV - primary, secondary, tertiary, quaternary structures
Quaternary structure not characteristic of all proteins. It arises from the combination of several macromolecules with a tertiary structure into a complex complex. For example, human blood hemoglobin is a complex of four protein macromolecules (Fig. 10).
This complexity of the structure of protein molecules is associated with a variety of functions inherent in these biopolymers.
Violation of the natural structure of the protein is called denaturation (fig. 11). It can occur under the influence of temperature, chemicals, radiant energy, and other factors. With a weak effect, only the quaternary structure breaks down, with a stronger one, the tertiary structure, and then the secondary one, and the protein remains in the form of a polypeptide chain.
Fig. 10. Scheme of the structure of the hemoglobin molecule
This process is partially reversible: if the primary structure is not destroyed, then the denatured protein is able to restore its structure. It follows from this that all structural features of the protein macromolecule are determined by its primary structure.
Besides simple proteinsconsisting only of amino acids, there is also complex proteins, which may include carbohydrates ( glycoproteins), fats ( lipoproteins), nucleic acids ( nucleoproteins) and etc.
The role of proteins in cell life is enormous. Modern biology has shown that the similarities and differences between organisms are ultimately determined by a set of proteins. The closer organisms are to each other in a systematic position, the more similar their proteins are.
Fig. 11. Protein denaturation
Proteins, or proteins. Simple and complex proteins. Amino acids. Polypeptide. Primary, secondary, tertiary and quaternary structures of proteins
Questions
1. What substances are called proteins or proteins?
2. What is the primary structure of a protein?
3. How are secondary, tertiary and quaternary protein structures formed?
4. What is protein denaturation?
5. On what basis are proteins divided into simple and complex?
Tasks
You know that the protein in a hen's egg is made up mainly of proteins. Think about the change in the protein structure of a boiled egg. Give other examples you know of when the structure of a protein can change.
§ 8. Functions of proteins
1. What is the function of carbohydrates?
2. What functions of proteins do you know?
Proteins perform extremely important and varied functions. This is possible largely due to the variety of forms and composition of proteins themselves.
One of the most important functions of protein molecules is construction (plastic). Proteins are part of all cell membranes and cell organelles. The walls of blood vessels, cartilage, tendons, hair and nails are mainly composed of protein.
Of great importance is catalytic, or enzymatic, protein function... Special proteins - enzymes are capable of accelerating biochemical reactions in the cell tens and hundreds of millions of times. About a thousand enzymes are known. Each reaction is catalyzed by a specific enzyme. You will learn more about this below.
Motor function carry out special contractile proteins. Thanks to them, cilia and flagella move in protozoa, chromosomes move during cell division, muscles contract in multicellular organisms, and other types of movement in living organisms are improved.
It is important transport function proteins. So, hemoglobin carries oxygen from the lungs to the cells of other tissues and organs. In addition to hemoglobin, muscles have another gas-transporting protein - myoglobin. Serum proteins promote the transfer of lipids and fatty acids, various biologically active substances. Transport proteins in the outer membrane of cells carry various substances from the environment into the cytoplasm.
Specific proteins perform protective function... They protect the body from the invasion of foreign proteins and microorganisms and from damage. Thus, antibodies produced by lymphocytes block foreign proteins; fibrin and thrombin protect the body from blood loss.
Regulatory function inherent in proteins - hormones... They maintain constant concentrations of substances in the blood and cells, participate in growth, reproduction and other vital processes. For example, insulin regulates blood sugar levels.
Proteins also have signal function... Proteins are built into the cell membrane that can change their tertiary structure in response to environmental factors. This is how signals are received from the external environment and information is transmitted to the cell.
Proteins can do energy function, being one of the energy sources in the cell. With the complete breakdown of 1 g of protein to final products, 17.6 kJ of energy is released. However, proteins are rarely used as a source of energy. Amino acids released when protein molecules are broken down are used to build new proteins.
Protein functions: building, motor, transport, protective, regulatory, signaling, energy, catalytic. Hormone. Enzyme
Questions
1. What explains the variety of functions of proteins?
2. What functions of proteins do you know?
3. What is the role of hormone proteins?
4. What is the function of enzyme proteins?
5. Why are proteins rarely used as an energy source?
§ 9. Nucleic acids
1. What is the role of the nucleus in the cell?
2. With which organelles of the cell is the transmission of hereditary characteristics associated?
3. What substances are called acids?
Nucleic acids (from lat. nucleus - nucleus) were first found in the nuclei of leukocytes. Subsequently, it was found that nucleic acids are contained in all cells, and not only in the nucleus, but also in the cytoplasm and various organelles.
There are two types of nucleic acids - deoxyribonucleic (abbreviated DNA) and ribonucleic (abbreviated RNA). The difference in names is due to the fact that the DNA molecule contains a carbohydrate deoxyribose, and the RNA molecule - ribose.
Nucleic acids - biopolymers composed of monomers - nucleotides... Monomers-nucleotides of DNA and RNA have a similar structure.
Each nucleotide consists of three components, linked by strong chemical bonds. it nitrogenous base, carbohydrate (ribose or deoxyribose) and phosphoric acid residue (fig. 12).
Part dNA molecules four types of nitrogenous bases are included: adenine, guanine, cytosine or thymine... They determine the names of the corresponding nucleotides: adenyl (A), guanyl (G), cytidyl (C) and thymidyl (T) (Fig. 13).
Fig. 12. Diagram of the structure of nucleotides - monomers of DNA (A) and RNA (B)
Each DNA strand is a polynucleotide consisting of several tens of thousands of nucleotides.
The DNA molecule has a complex structure. It consists of two spirally twisted chains, which are connected to each other by hydrogen bonds along their entire length. This structure, inherent only to DNA molecules, is called double helix.
Fig. 13. DNA nucleotides
Fig. 14. Complementary connection of nucleotides
During the formation of a DNA double helix, the nitrogenous bases of one chain are arranged in a strictly defined order against the nitrogenous bases of the other. In this case, an important regularity is revealed: the thymine of the other chain is always located opposite the adenine of one chain, cytosine is against the guanine, and vice versa. This is because the adenine and thymine nucleotide pairs, as well as guanine and cytosine, strictly correspond to each other and are complementary, or complementary (from lat. complementum - addition), to each other. And the pattern itself is called principle of complementarity... In this case, two hydrogen bonds always arise between adenine and thymine, and three between guanine and cytosine (Fig. 14).
Consequently, in any organism, the number of adenyl nucleotides is equal to the number of thymidyl nucleotides, and the number of guanyl nucleotides is equal to the number of cytidyl nucleotides. Knowing the sequence of nucleotides in one DNA strand, according to the principle of complementarity, it is possible to establish the order of nucleotides in another strand.
With the help of four types of nucleotides, all information about the organism is recorded in DNA, which is inherited by the next generations. In other words, DNA is the carrier of hereditary information.
DNA molecules are mainly found in the nuclei of cells, but a small amount is found in mitochondria and plastids.
The RNA molecule, in contrast to the DNA molecule, is a polymer consisting of a single chain of much smaller dimensions.
RNA monomers are nucleotides consisting of ribose, a phosphoric acid residue and one of four nitrogenous bases. Three nitrogenous bases - adenine, guanine and cytosine - are the same as in DNA, and the fourth is uracil.
The RNA polymer is formed through covalent bonds between ribose and the phosphoric acid residue of adjacent nucleotides.
There are three types of RNA, differing in structure, size of molecules, location in the cell, and functions performed.
Ribosomal RNA (rRNA) are part of the ribosomes and participate in the formation of their active centers, where the process of protein biosynthesis takes place.
Transport RNA (tRNA) - the smallest in size - transport amino acids to the site of protein synthesis.
Information, or messenger, RNA (mRNA) are synthesized at the site of one of the chains of the DNA molecule and transmit information about the structure of the protein from the cell nucleus to the ribosomes, where this information is realized.
Thus, different types of RNA represent a single functional system aimed at the implementation of hereditary information through protein synthesis.
RNA molecules are found in the nucleus, cytoplasm, ribosomes, mitochondria and plastids of the cell.
Nucleic acid. Deoxyribonucleic acid, or DNA. Ribonucleic acid, or RNA. Nitrogenous bases: adenine, guanine, cytosine, thymine, uracil, nucleotide. Double helix. Complementarity. Transport RNA (tRNA). Ribosomal RNA (rRNA). Messenger RNA (mRNA)
Questions
1. What is the structure of a nucleotide?
2. What is the structure of the DNA molecule?
3. What is the principle of complementarity?
4. What is common and what are the differences in the structure of DNA and RNA molecules?
5. What types of RNA molecules do you know? What are their functions?
Tasks
1. Make a paragraph outline.
2. Scientists have found that a fragment of a DNA strand has the following composition: C-G G A A T T C C. Using the principle of complementarity, complete the second strand.
3. In the course of the study, it was found that in the studied DNA molecule adenines make up 26% of the total number of nitrogenous bases. Count the number of other nitrogenous bases in this molecule.
American scientists managed to create a molecule that could be the ancestor of modern molecular carriers of hereditary information in a living cell - nucleic acids. It was named TNK, since this substance contains the four-carbon sugar tetrose. It is assumed that in the process of evolution it was from it that the DNA and RNA we know came from.
Until now, scientists engaged in the reconstruction of events that occurred on Earth about four billion years ago cannot answer one simple and at the same time very important question - how did deoxyribonucleic acid, or, more simply, DNA, appear?
Indeed, without this molecule, the first living cells (or their predecessors) could not store information about the structure of proteins, which is necessary for self-reproduction. That is, without DNA, life simply would not be able to spread across our planet, both in space and in time.
Numerous experiments have shown that DNA by itself cannot assemble, in what conditions do not put all its "spare parts". In order to create this molecule, the activity of several dozen enzyme proteins is required. And if this is so, then immediately in the reasoning of evolutionists a vicious circle arises like the problem of the primacy of the chicken and the egg: where could enzymes come from if there is no DNA itself? After all, information about their structure is recorded precisely in this complex molecule.
However, recently some molecular biologists have proposed a way out of this impasse: they believe that previously hereditary information was stored in the DNA "sister", ribonucleic acid, or RNA. Well, this molecule is capable of self-copying under certain conditions, and numerous experiments confirm this (you can read more about this in the article "In the beginning there was ... ribonucleic acid").
It seems that a way out was found - at first ribozymes (this is the name of RNA molecules with enzymatic activity) copied themselves and along the way, mutating, "acquired" information about new useful proteins. After some time, this information accumulated so much that RNA "understood" one simple thing - now it is no longer necessary to do the rather complicated work of self-copying itself. And soon the next cycle of mutations turned RNA into a more complex, but at the same time stable DNA, which was no longer involved in such "nonsense".
However, the final answer to the question of how nucleic acids appeared was still not found. Since it still remained unclear how the very first RNA appeared with the ability to copy itself. After all, even it, as shown by experiments, is not capable of self-assembly - its molecule is also very difficult for this.
Some molecular biologists, it is true, suggested that, perhaps, in those distant times, another nucleic acid could exist, arranged more simply than DNA and RNA. And it was she who at first was a molecule that stores information.
However, it is rather difficult to verify this assumption, since at present there are no other "keepers" of information from the group of these acids, except for DNA and RNA. Nevertheless, modern methods biochemistry makes it possible to recreate such a compound, and then experimentally test whether it is suitable for the role of the "main molecule of life" or not.
And recently, scientists from the University of Arizona (USA) suggested that the common ancestor of DNA and RNA could be TNK, or tetrosonucleic acid. It differs from its descendants in that the "sugar-phosphate bridge" of this substance, which holds the nitrogenous bases (or nucleotides) together, does not contain pentose, a sugar of five carbon atoms, but four-carbon tetrose. And this type of sugar is much simpler than the five-carbon rings of DNA and RNA. And, most importantly, they can assemble themselves - from two identical two-carbon pieces.
American biochemists tried to create several short tetrose molecules and, in the process, found out that this does not require the use of a massive and complex enzymatic apparatus at all - under certain conditions, the acid was collected in a saturated solution from "spare parts" using only two enzymes.
That is, it really could appear at the very beginning of the formation of life. And while the first living organisms could not acquire an enzymatic apparatus capable of synthesizing RNA and DNA, then it was TNK that was the keeper of hereditary information.
But could, in principle, this molecule have played such a crucial role? Now this cannot be directly verified, since there are no proteins capable of reading information from TNCs. However, Arizona molecular biologists decided to take a different route. They conducted a curious experiment - they tried to connect strands of DNA and TNCs with each other. As a result, a hybrid molecule was obtained - in the middle of the DNA chain there was a fragment of TNC with a length of 70 nucleotides. Interestingly, this molecule was capable of replication, that is, self-copying. And this property is essential for any molecular information carrier.
Moreover, scientists have shown that the TNK molecule may well combine with a protein and, accordingly, obtain enzymatic properties. The researchers conducted a series of experiments that demonstrated that a structure that specifically binds to the thrombin protein could be obtained from TNC: the TNK chain was formed on the DNA chain, but after the DNA left, it did not lose its structural features and continued to specifically retain the protein.
The TNC fragment was 70 nucleotides in length, which is quite enough to create unique "landing sites" for enzyme proteins. That is, from TNC, something like a ribozyme could also have turned out (remember that it is made up of RNAs associated with a protein).
So, experiments have shown that TNK could well be the ancestor of DNA and RNA. The latter may have formed somewhat earlier as a result of a series of mutations that led to the replacement of tetrose with pentose. And then, using natural selection, it turned out that ribonucleic acid is more stable and stable than its tetrose predecessor (tetroses are indeed very unstable to a number of chemical influences). And thus the descendant competitively pushed his ancestor out of the niche of the molecular information carrier.
The question arises - could the TNC also have some ancestor containing a simpler sugar than tetrose? Most likely not, and here's why. Only starting with four carbon atoms can sugars form cyclic structures, three-carbon carbohydrates are incapable of this. Well, without this, nucleic acid is not formed - only cyclic sugar molecules can hold all the other components of this substance. So it looks like TNK really came first.
It should be noted that the authors of the work do not at all claim that "everything was exactly like that." Strictly speaking, they only proved the possibility of the existence of an ancestral form of ribonucleic acids, such as TNK (which, by the way, does not occur in the modern world in the natural environment). The value of the discovery lies in the fact that one of the probable ways of evolution of molecular carriers of hereditary information was shown. Well, and, finally, the old dispute about which appeared first - nucleic acid or protein ...
Question 1. What processes are scientists investigating at the molecular level?
At the molecular level, the most important vital processes of the organism are studied: its growth and development, metabolism and energy conversion, storage and transmission of hereditary information, variability.
Question 2. What elements prevail in the composition of living organisms?
A living organism contains more than 70-80 chemical elements, but carbon, oxygen, hydrogen and nitrogen prevail.
Question 3. Why are molecules of proteins, nucleic acids, carbohydrates and lipids considered as biopolymers only in the cell?
Molecules of proteins, nucleic acids, carbohydrates and lipids are polymers, as they are composed of repeating monomers. But only in a living system (cell, organism) do these substances manifest their biological essence, possessing a number of specific properties and performing many important functions. Therefore, in living systems, such substances are called biopolymers. Outside a living system, these substances lose their biological properties and are not biopolymers.
Question 4. What is meant by the universality of biopolymer molecules?
The properties of biopolymers depend on the number, composition and arrangement of their constituent monomers. The possibility of changing the composition and sequence of monomers in the polymer structure allows a huge variety of biopolymer variants to exist, regardless of the species of the organism. All living organisms have biopolymers built according to a single plan.
1.1. Molecular level: general characteristics
4.4 (87.5%) 8 votesSearched on this page:
- what processes are scientists investigating at the molecular level
- what is meant by the universality of biopolymer molecules
- what elements prevail in the composition of living organisms
- why protein molecules, nucleic acids of carbohydrates and lipids are considered as biopolymers only in the cell
- why protein molecules nucleic acids carbohydrates and lipids
Question 1. What processes are scientists investigating at the molecular level?
At the molecular level, the most important vital processes of the organism are studied: its growth and development, metabolism and energy conversion, storage and transmission of hereditary information, variability. The elementary unit at the molecular level is a gene - a fragment of a nucleic acid molecule, in which a quantity of biological information defined in qualitative and quantitative terms is recorded.
Question 2. What elements prevail in the composition of living organisms?
There are more than 70-80 chemical elements in the composition of a living organism, however, carbon, oxygen, hydrogen, nitrogen and phosphorus prevail.
Question 3. Why are molecules of proteins, nucleic acids, carbohydrates and lipids considered as biopolymers only in the cell?
Molecules of proteins, nucleic acids, carbohydrates and lipids are polymers, as they are composed of repeating monomers. But only in a living system (cell, organism) do these substances manifest their biological essence, possessing a number of specific properties and performing many important functions. Therefore, in living systems, such substances are called biopolymers. Outside a living system, these substances lose their biological properties and are not biopolymers.
Question 4. What is meant by the universality of biopolymer molecules?
Regardless of the level of complexity and functions performed in the cell, all biopolymers have the following features:
their molecules have few long branches, but many short ones;
polymer chains are strong and do not fall apart spontaneously;
are able to carry a variety of functional groups and molecular fragments that provide biochemical functional activity, that is, the ability to carry out the biochemical reactions and transformations necessary for a cell in an intracellular solution;
have flexibility sufficient for the formation of very complex spatial structures necessary for the performance of biochemical functions, that is, for the operation of proteins as molecular machines, nucleic acids as programming molecules, etc .;
the C-H and C-C bonds of biopolymers, despite their strength, are simultaneously accumulators of electronic energy.
The main property of biopolymers is the linearity of polymer chains, since only linear structures are easily encoded and “assembled” from monomers. In addition, if a polymer thread has flexibility, then it is quite easy to form the desired spatial structure from it, and after the molecular machine built in this way is cushioned, broken, it is easy to disassemble it into its constituent elements in order to use them again. The combination of these properties is found only in carbon-based polymers. All biopolymers in living systems are capable of performing certain properties and performing many important functions. The properties of biopolymers depend on the number, composition and arrangement of their constituent monomers. The possibility of changing the composition and sequence of monomers in the polymer structure allows a huge variety of biopolymer variants to exist, regardless of the species of the organism. All living organisms have biopolymers built according to a single plan.
